1. Field of the Invention
The invention is generally related to the area of optical communications. In particular, the invention is related to optical devices using one or more concave mirrors to process light beams and the making thereof. The optical devices include, but may not be limited to, multiplexing devices and adding/dropping devices.
2. The Background of Related Art
The future communication networks demand ever increasing bandwidths and flexibility to different communication protocols. Fiber optic networks are becoming increasingly popular for data transmission due to their high speed and high capacity capabilities. Wavelength division multiplexing (WDM) is an exemplary technology that puts data from different sources together on an optical fiber with each signal carried at the same time on its own separate light wavelength. Using the WDM system, up to 80 (and theoretically more) separate wavelengths or channels of data can be multiplexed into a light stream transmitted on a single optical fiber. To take the benefits and advantages offered by the WDM system, there require many sophisticated optical network elements.
Optical add/drop devices are those elements often used in optical systems and networks. For example, an exchanging of data signals involves the exchanging of matching wavelengths from two different sources within an optical network. In other words, the multi-channel signal would drop a wavelength while simultaneously adding a channel with a matching wavelength at the same network node.
A commonly used WDM device is what is called a three-port device. FIG. 1 shows a functional diagram of a three-port add/drop device 100. The optical device 100 includes a common (C) port 102, a reflection (R) port 104, and a transmission (T) port 106. When the device 100 is used as a multiplexer (i.e., to add a signal at a selected wavelength λK to other signals at wavelengths other than the selected wavelength λK), the T-port 106 receives a light beam at the selected wavelength λK that is to be multiplexed into a group of beams at wavelengths λ1, λ2, . . . λN excluding the selected wavelength λK coupled in from the R-port 104. The C-port 102 subsequently produces a multiplexed signal including all wavelengths (λ1, λ2, . . . λK, . . . λN).
Likewise, when the optical device 100 is used to demultiplex signals, the C-port 102 receives a group of signals with wavelengths λ1, λ2, . . . λK,  . . . λN. The T-port 106 passes a signal with the selected wavelength λK while the R-port 104 subsequently bypasses the rest of the input signals wavelengths λ1, λ2, . . . λN except for the selected wavelength λx.
FIG. 2 shows an exemplary internal configuration 110 of the optical device 100 of FIG. 1. As shown in FIG. 2, there is a first GRIN lens 112, an optical filter 114 (e.g., a multi-layer thin film filter) and a second GRIN lens 116. In general, a dual-fiber pigtail is provided in a holder 118 (e.g., a dual-fiber pigtail collimator) and coupled to or positioned towards the first GRIN lens 112, and a single-fiber pigtail is provided in a second holder 120 and coupled to or positioned towards the second GRIN lens 116. Essentially the two GRIN lenses 112 and 116 accomplish the collimating means for coupling an optical signal with multi channels or wavelengths in and out of the C port 102, the R port 104, or the T port 106. In general, the three-port device 100 is known to have a very low coupling loss from the C-port to both the R-port and the T-port for use as a demultiplexing device, or vise versa as a multiplexing device.
Such three-port WDM device has fewer components involved and therefore a larger tolerance window for high yield. However, it has been well-known that there is substantial disadvantage of such WDM device made through the traditional 3-port device: it is of high cost, requiring two GRIN lenses, one dual-fiber pigtail, one-single fiber pigtail, an optical filter, and packaging glass tubes and/or metal tubes.
In applications, when used to form multi-channel multiplexiers or demultiplexiers, or add/drop multiplexiers (OADMs), a plurality of such three-port devices need to be cascaded together through fiber splicing. The resulting costs of the multi-channel WDM or multi-channel OADM are very high. In general a package, typically a cassette, or a chassis, will be used to enclose the fiber spliced and the cascaded 3-port devices, adding additional costs.
Accordingly, there is a great need for improved optical devices that are amenable to low cost, especially for individual WDM device, as well as for cascaded, multi-channel WDM devices.